1. Field of the Invention
The present invention relates to a method for the elimination, in a receiver, of incident beams resulting from multipaths, and to a device for implementing this method.
2. Description of the Related Art
Systems which nowadays make it possible to strengthen resistance to multipaths in radionavigation receivers are most of the time based on the use of more or less particular correlators (narrow correlator, double delta correlator, etc.), making it possible to ignore multipaths delayed by a greater or lesser distance, always less than twice the chip length of the pseudorandom code used T, that is to say the period of the clock signals of the codes of the radionavigation signals (for example, for signals of the “Global Positioning System”, GPS type, 1 chip=1 μs in C/A code, i.e. ˜300 m, or 100 ns in P code, i.e. ˜30 m). Nevertheless, for multipaths with small delays relative to the chip length, these correlators turn out to be inefficient.
U.S. Pat. No. 6,175,327 discloses a method for the elimination of interference in receivers of GPS radionavigation signals. This method uses a power inversion technique that calls upon an array of n antennas whose signals are individually weighted by inversion of a cross-correlation matrix and use of a canonical constraint not representing a particular reception direction, but a criterion of “minimization of the power received taking account of all the directions in space”. This known method for eliminating interference is applicable only to signals whose power referred to each sensor is greater than the level of power due to thermal noise. Furthermore, this processing is carried out without prior knowledge of the direction of arrival of the signal that one wishes to eliminate. It is therefore impossible with this known method alone to determine the direction of arrival of one or more signals due to multipaths, or to eliminate them: their power level referred to the input of the receiver is in fact lower than the power level of the main signal (direct path), the power level of which is itself smaller than that of the thermal noise generated in the spectral processing band (passband at the input of the receiver).
An object of the present invention is a method making it possible to eliminate on reception a signal due to multipaths and coming from a direction other than that of the transmitter, whatever its delay with respect to the signal coming directly from the transmitter.